# Test 3: Time Stability of the Coefficient Surface

| DV | Period | Z₁ (base) | Z₁×High | Z₁×Low | Z₁×OECD | N |
|---|---|---|---|---|---|---|
| ca_gdp | Full | 29.765** | 64.946* | -75.215** | -52.375 | 7624 |
| ca_gdp | Pre-GFC | 34.803** | 51.963 | -94.071** | -61.707 | 4419 |
| ca_gdp | Post-GFC | 4.936 | 111.230** | -88.777 | -19.814 | 3021 |
| gross_savings_gdp | Full | 114.147*** | -0.364 | 60.121 | -119.086* | 6642 |
| gross_savings_gdp | Pre-GFC | 128.843*** | -36.259 | 42.179 | -133.500 | 3846 |
| gross_savings_gdp | Post-GFC | 124.643*** | 72.647 | 88.604 | -159.130 | 2633 |

*Pre-GFC: <=2007. Post-GFC: >=2009. Stable surface = similar interaction signs and magnitudes.*
